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2020 / 2021 Edition

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Engineering Safer Conveyors: Art Meets Science

First published in the July 2021 issue of Quarry Management

Martin Engineering explain why the most effective way to mitigate risks is to design the hazard out of the conveyor component or system

All new conveyor systems will inevitably succumb to the punishing bulk handling environment and begin the slow process of degradation. The system will eventually require more time and labour for maintenance and be subject to shorter spans between outages, longer periods of downtime and an ever-increasing cost of operation. This period is also accompanied by an increased chance of injury or fatality as workers are progressively exposed to the equipment to perform cleaning and maintenance and to fabricate short-term fixes to long-term problems. A total system replacement is cost prohibitive, but to remain compliant and/or meet ever-increasing production demands, upgrades and repairs are unavoidable.

When examining the safety of a system, improving efficiency and reducing risk can be achieved by utilizing a hierarchy of control methods for alleviating hazards. The consensus among safety professionals is that the most effective way to mitigate risks is to design the hazard out of the component or system. This usually requires a greater initial capital investment than short-term fixes but yields more cost-effective and durable results.

The science: Hierarchy of control methods

Examining the US Occupational Safety and Health Administration (OSHA) accident database reveals the dangers of working around conveyors[1]. Studies have revealed that the most accidents happen near locations where cleaning and maintenance activities most frequently take place, eg the take-up pulley, tail pulley and head pulley.

Designs should be forward-thinking, exceeding compliance standards and enhancing operators’ ability to incorporate future upgrades cost-effectively and easily by taking a modular approach. Designing hazards out of the system means alleviating causes with the intent to bolster safety on a conveyor system, but the methods of protecting workers can vary greatly. In many cases it will be necessary to use more than one control method, by incorporating lower-ranked controls. However, these lower-ranking approaches are best considered as support measures, rather than solutions in and of themselves.

PPE includes respirators, safety goggles, blast shields, hard hats, hearing protectors, gloves, face shields, footwear etc, which provide a barrier between the wearer and the hazard. Downsides are that these items can be worn improperly, may be uncomfortable to use through an entire shift, can be difficult to monitor and may offer a false sense of security. But the bottom line is that they do not address the source of the problem.

Administrative controls (changes to the way people work) create policy that articulates a commitment to safety, but written guidelines can be easily shelved and forgotten. These controls can be taken a step further by establishing ‘active’ procedures to minimize the risks. For example, supervisors can schedule shifts that limit exposure and require more training for personnel, but these positive steps still do not remove the exposure and causes of hazards.

Warning signage is generally required by law, so this is less of a method than a compliance issue. Signs should be posted in plain sight, clearly understood and washed when dirty or replaced when faded. Like most lower-tier methods, signs do not remove the hazard and are easily ignored.

Installing systems such as Engineering controls that allow remote monitoring and control of equipment – or Guards such as gates and inspection doors that obstruct access – greatly reduce exposure but, again, do not remove the hazard.

Using the Substitute method replaces something that produces a hazard with a piece of equipment or change in material that eliminates the hazard. For example, manual clearing of a clogged hopper could be replaced by installing remotely triggered air cannons.

Examples of Eliminate by Design are longer, taller and tightly sealed loading chutes to control dust and spillage or heavy-duty primary and secondary cleaners to minimize carryback. By using hazard identification and risk-assessment methods early in the design process, engineers can create the safest, most efficient system for the space, budget and application.

Economic analysis of Prevention through Design

Another way of saying ‘Eliminate by Design’ is ‘Prevention through Design’ (PtD), the term used by The National Institute of Occupational Safety and Health (NIOSH). As a department of the US Centers for Disease Control (CDC), the organization spearheaded the PtD initiative[3]. In its report, the Institute points out that, while the underlying causes vary, studies of workplace accidents implicate ‘system design’ in 37% of job-related fatalities.

Cost is most often the main inhibitor to PtD, which is why it is best to implement safer designs in the planning and initial construction stages, rather than retrofitting a system later. The added cost of PtD is often less than an additional 10% of the engineering cost but has enormous benefits in terms of improved safety and increased productivity.

The cost of PtD initiatives after initial construction can be three to five times as much as when the improvement is incorporated in the design stage. The biggest cause of expensive retroactive improvements is cutting corners, initially by seeking lowest-bid contracts.

Low-bid process and life-cycle cost

Although the policy is generally not explicitly stated by companies, the low-bid process is usually an implied rule that is baked  into a company’s culture. It encourages bidders to follow a belt conveyor design methodology that is based on getting the maximum load on the conveyor belt and the minimum compliance with regulations using the lowest-price materials, components and manufacturing processes available.

When companies buy on price, however, the benefits are often short-lived and costs increase over time, eventually resulting in losses. In contrast, when purchases are made based on lowest long-term cost (life-cycle cost), benefits usually continue to accrue and costs are lower, resulting in a net savings over time[4].

The art: Design hierarchy 

Rather than meeting minimum compliance standards, the conveyor system should exceed all code, safety and regulatory requirements using global best practices. By designing the system to minimize risk and the escape and accumulation of fugitive material, the workplace is made safer and the equipment is easier to maintain.

Life-cycle costing should play into all component decisions. Buying on life-cycle cost and anticipating the future use of problem-solving components in the basic configuration of the conveyor provides improved safety and access, without increasing the structural steel requirements or significantly increasing the overall price. It also raises the possibility of easier system upgrades in the future.

Best practices: The ‘Evolved Basic Conveyor’

Using the hierarchy of controls along with the design hierarchy, engineers will be able to construct an ‘Evolved Basic Conveyor’ that meets the needs of modern production and safety demands. Built competitively with a few modifications in critical areas, an Evolved Basic Conveyor is a standard bulk material handling conveyor designed to allow easy retrofitting of new components that improve operation and safety, solving or preventing common maintenance problems.

Installing or providing for maintenance-minded solutions in the loading zone can greatly improve safety and reduce man-hours and downtime. These components include slide-in/slide-out idlers, impact cradles and support cradles. On larger conveyors, maintenance aids such as overhead monorails or jib cranes assist in the movement and replacement of components. Also, designers should ensure adequate access to utilities – typically electricity and/or compressed air – to facilitate maintenance and performance. Next-generation conveyor designs may even feature a specially engineered idler capped with an independent power generator that uses the conveyor’s movement to generate power for a wide array of autonomous equipment.

Dust, spillage and belt tracking are top concerns for many safety professionals. Field tests have shown that enlarged skirtboards and engineered settling zones promote dust settling and reduce fugitive material. Curved loading and discharge chutes control the cargo transfer for centred placement and reduced turbulence. As the load is centred on the belt, guides ensure even travel through the take-up to promote consistent belt tracking.

Any transfer point is prone to build-up and clogging under certain conditions, be it ambient humidity, material wetness, volume or surface grade. Flow aids such as vibrators or air cannons on chutes can sustain material movement, improve equipment life and reduce the safety hazards associated with manually clearing clogged equipment.

Conclusion

Engineering safer conveyors is a long-term strategy. Although design absorbs less than 10% of the total budget of a project, additional upfront engineering and applying a life cycle-cost methodology to the selection and purchase of conveyor components will prove beneficial.

By encouraging the use of the hierarchy of controls at the planning stage, along with the design hierarchy at the design stage, the system will likely meet the demands of modern production and safety regulations, with a longer operational life, fewer stoppages and a lower cost of operation.

*All figures Copyright 2021 Martin Engineering

REFERENCES

  1. Conveyor Accident Database, OSHA, US Dept. of Labor, Washington DC, 2018.
  2. ‘Foundations for Conveyor Safety’, Ch. 31, pp 404-440, Martin Engineering, Worzalla Publishing Co., 2016.
  3. HOWARD, J.M.D.: ‘Prevention through Design: Plan for the National Initiative’, National Institute of Occupational Safety and Health (NIOSH), US Centers for Disease Control (CDC), Dept. of Health and Human Services. Washington DC, 2010.
  4. SWINDERMAN, R.T.: ‘The Economics of Workplace Safety: Putting a price on material handling mishaps’, Coal Age, vol. 123, no. 3, pp 28-31, April 2018.
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